1. Field of the Invention
This invention relates to sun powered electrical generators, and more particularly to a method and apparatus for changing the spectral characteristics of the sun rays before directing them onto the solar cells, to make them more closely match the response function of the solar cells.
2. Description of the Prior Art
As is well known, a solar battery is a dc power source made up of several solar cells connected in series or parallel or both, to deliver useful amounts of power when illuminated by sunlight. Heavy duty photo-electric batteries are used in space satellites, control devices, emergency telephone power supplies, portable radios, and other places. Generally speaking a solar cell is a heavy duty photovoltaic cell; that is, a self-generating cell that can produce usefully high voltage and current when exposed to sunlight. One known type of solar cell is the silicon cell. This type of photovoltaic cell delivers the highest output for a given light intensity. In a typical silicon cell an n-silicon layer is applied to a metal back plate which becomes the negative output electrode. A thin p-type layer then is formed on, or diffused into, the exposed face of the n-type layer. Finally, for ohmic contact, a sprayed-on (or plated) strip is applied to the p-type layer to serve as the positive output electrode.
A typical solar battery comprises one or more planar panels of photovoltaic cells which in use are oriented to face towards the sun. Not all of the solar energy received by the solar battery is converted to electricity. Some of it merely heats the solar battery and other portions of it are either reflected back towards the sun or passes through the solar battery.
In accordance with the present invention, the solar spectrum is converted to a new spectrum which more closely matches the response function of the solar cells, so that less heat is generated and more electricity produced by the photon energy which reaches the solar cells. Also, according to an aspect of the invention, the long wave length photon energy which is allowed to pass through conventional solar batteries is collected and utilized for the purpose of further increasing the efficiency of the system.
The present invention involves the use of reflectors or mirrors for concentrating solar energy at the focus of the reflector. This practice is per se old and has been utilized in solar heating systems wherein an object to be heated (i.e. a fluid conduit) is located at the focus of a curved reflector. It is also known per se to reflect infrared photon energy back towards a source of radiant energy, as is disclosed in U.S. Pat. No. 3,331,707, granted July 18, 1967 to John J. Werth. However, it is not known to increase the efficiency of a solar battery system by changing the spectral characteristics of the photon energy received from the sun before directing it onto solar cells for generating useful electricity.